This application relates to osteotomy procedures and, more particularly, to methods and systems for planning and performing osteotomy procedures.
An osteotomy is a surgical procedure in which a bone is cut and reconfigured, often to correct a misaligned joint. Misaligned joints can cause osteoarthritis, or degradation of articular cartilage, resulting in pain, stiffness, and swelling. By realigning the joint, an osteotomy procedure relieves pressure on a portion of the joint by shifting the load-bearing axis.
Osteotomy procedures to reconfigure the tibia or femur can relieve pain and other symptoms resulting from osteoarthritis of the knee. In an open wedge osteotomy, a cut is made through a portion of the bone and the opposing surfaces of the cut are pulled apart to create a wedge-shaped opening, which can then be filled by bone graft. In a closing wedge osteotomy, a wedge-shaped portion of bone is removed, and the opposing surfaces are brought together to close the opening.
Conventional osteotomies are technically challenging procedures to plan and perform. One current planning method includes drawing a planned cut or wedge to be removed onto a two-dimensional image of the joint. There are numerous challenges associated with accurately planning a surgical procedure using a two-dimensional image when the surgery is executed on a three-dimensional portion of the anatomy. One difficulty associated with conventional planning techniques includes the lack of tools to analyze the surgical plan in terms of the structural soundness (i.e. integrity) of the planned post-operative bone. Without analyzing the predicted structural soundness of the bone, osteotomies performed according to plan may result in post-operative fractures of the tibia.
In addition to the challenges of planning osteotomy procedures, surgeons also face challenges during implementation. During high tibial osteotomies, for example, the surgeon attempts to achieve a specific desired angle between the femur and tibia (e.g. the femoral-tibial alignment angle). Studies have shown that a femoral-tibial angle of 7-13 degrees of valgus alignment results in beneficial long-term clinical outcomes. High tibial osteotomies attempt to achieve the desired femoral-tibial angle by adding bone to the tibia (open wedge osteotomy) or by removing bone from the tibia (closing wedge osteotomy). In both open and closing wedge osteotomies, it is necessary to calculate the “wedge correction angle” based on the desired femoral-tibial angle. In an open wedge osteotomy, the wedge correction angle refers to the desired final angle between the resected surfaces. In a closing wedge osteotomy, the “wedge correction angle” refers to the initial angle between resected surfaces of the bone after removal of the wedge, but prior to bringing the resected surfaces together.
Often, it is difficult to determine whether the desired wedge correction angle, and therefore, the desired alignment between the two bones of the joint, has been achieved by the osteotomy procedure. This difficulty arises even during image-guided surgeries in which a navigation system tracks the bones of the joint. For example, during high tibial osteotomies, a navigation system tracks a marker attached to the tibia. However, once the surgeon cuts through all or a portion of the tibia and moves the resected surfaces relative to each other, the tracking system is no longer able to determine the pose (i.e. position and orientation) of the portion of the tibia on the non-tracked side of the cut. The surgeon therefore cannot rely on a display of the tracked bones to determine, for example, how far to increase the angle between the resected surfaces in an open wedge osteotomy.
Another challenge associated with conventional osteotomy procedures is lack of control of the saw blade used for cutting the bone, particularly in the anterior-posterior plane. Lack of adequate control can cause inaccuracies in the resulting alignment of the joint.
A further challenge associated with conventional osteotomy procedures results from the use of K-wires and fluoroscopy to verify the planned cutting plane. Resections of the bone may be performed by using K-wires as cutting guides. The K-wires are pushed into the bone, and fluoroscopic images are taken of the bone and K-wires to evaluate, for example, the planned placement of the cutting plane and fixation plate screws. This portion of the planning process exposes the patient to additional radiation.